Duplicate code exemple

Remove duplicate code exemple
Update introduction.rst

Console component is in symfony/console package, not symfony/config.
Updating 2.3 with #399
Merge pull request #402 from gregquat/2.3

Updating 2.3 with #399
Merge pull request #403 from symfony-fr/2.3

Updating 2.3 with #399
Merging #403 from 2.3
Merge pull request #404 from gregquat/2.4

Merging #403 from 2.3
Merging #401
Merge pull request #405 from gregquat/2.3

Merging #401
Merge pull request #406 from symfony-fr/2.3

Merging #401
Merge pull request #401 from FGM/patch-1

Update introduction.rst
Merge pull request #407 from symfony-fr/2.4

Merging 2.4 to master